Most firearms provide mechanisms to facilitate the automated handling of ammunition components as they are used. A firing cycle can include the stages of: stripping an unfired ammunition cartridge from a spring-loaded multi-cartridge magazine, chambering the cartridge; firing; extraction of the spent cartridge casing from the chamber; and, ejection of spent cartridge casing from the firearm. A blowback bolt mechanism uses some of the force of the pressurized gasses generated by the burning propellant in the cartridge to accomplish operation of the cycle in an automatic or semiautomatic way. Blowback style bolt action firearms have been around for many years.
Typically prior blowback style bolts, after being driven rearwardly by firing, will automatically spring back forwardly on a return stroke. During the forward return stroke, the rapidly moving bolt will strip the lead cartridge from a queue of unfired cartridges supplied by a spring-loaded magazine, and drive the stripped cartridge into the chamber. During the stripping and chambering process, the forward facing end of the bolt contacts the rear rim of the lead cartridge and must allow the rim to slide upward so that the rim becomes properly seated against the bolt by the time the bolt face reaches its fully forward firing position. If not handled precisely, the cartridge can rapidly become improperly oriented, leading to ammunition handling problems such as jamming.
Indeed, the main problem with conventional blowback style bolts is the temporary loss of control of the cartridge being loaded. Because the magazine typically supplies cartridges in a slightly “nose-up” orientation, the orientation of the stripped cartridge must change by the time the cartridge is chambered. While being stripped from the magazine and inserted into the barrel's chamber, there is a point where the velocity and control of the cartridge is temporarily lost as the cartridge rim slides over the edge of the driving ledge of the bolt, and falls into the piloting bore at the front end of the bolt. In addition, the loading impact and force to the cartridge is directed to a small peripheral area of the bolt, primarily about the leading edge of the bolt face, until the cartridge angle squares up to the bolt as it is piloting into the barrel bore, when the cartridge falls squarely into the bolt's cartridge pilot bore. During this time very little surface area of the cartridge is being contacted leading to loss of control. Such conventional bolts provide little if any lateral control of the cartridge during the loading process. As the cartridge is stripped from the magazine it can move about on the raised lip of the bolt until it is constrained by the chamber of the barrel late in the loading process where it finally forces the rim to fall into the counter bored seat for the cartridge as the bolt comes to rest against the barrel chamber. Such unpredictable moving about as a result of loss of control can lead to cartridge handling problems such as jamming and excessive wear.
Basic operation of any firearm bolt is to forcibly remove, or strip an unfired cartridge from a magazine, and transport it to the chamber of the barrel for firing. After firing the cartridge's projectile, the blow-back bolt moves away from the barrel's chamber controlling the rear of the cartridge until the point where the extractor and ejector mechanisms eject the spent cartridge casing from the bolt's path so the process can repeat. While stripping the cartridge from the magazine, spring loaded forces from the magazine's retention mechanics can exert lateral directional forces to the cartridge during the cartridge release. With prior art bolts, these lateral forces come to play more readily while the cartridge is being freed from the magazine at bolt velocity to seating into the barrel chamber. These forces can drive the cartridge laterally during loading and create issues from simple force vectored energy absorption slowing cyclic rates, to creating inconsistent load feeds, to complete load failures or “jamming” where the cartridge is cocked at an interference angle to the chamber, stopping the bolt from seating at the fire position. With prior art bolts the lateral forces are compounded by the lack of cartridge control of the rear section of the cartridge, at the rim, until the point in the loading process when the cartridge “falls” over the lip of the bolt into the counter bored seat for the cartridge where it continues the final short path to seating in the barrel's chamber.
Therefore, there is a need for cartridge stripping mechanism which addresses some or all of the above identified inadequacies.